Photopolymerization of vinylidene compounds with organic disulfides



Patented Jane 25, 1949 PHOTOPOLYMERIZATION OF VINYLIDENE COMPOUNDS WITHORGANIC DISULFIDES Lawrence Marion Richards, Wilmington, Del.,

assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, acorporation of Delaware No Drawing. Application August 21, 1943, SerialNo. 499,555

Claims.

This invention relates to the photopolymerization of unsaturated organiccompounds.

The polymerization of ethylenically unsaturated organic compounds underthe influence of light is well known in the art. It is also well knownthat certain adjuvants are photopolymerization catalysts and have beenemployed in the photopolymerization of ethylenically unsaturated organiccompounds but none of these have attained any degree of practicalsignificance.

This invention has as an object the provision of a process for thephotopolymerization of polymerizable organic compounds in the presenceof new and improved photopolymerization catalysts. Other objects willappear hereinafter.

These objects are accomplished by the following invention whichcomprises irradiating, with light of wave lengths in the range from 2500to 5000 Angstrom units, a composition comprising a photopolymerizablevinyl or vinylidene compound containing at least one CH2=C groupactivated by direct attachment to a different negative group, that is,halogen, k0, CN, -CEC-, O-, or aryl, and from 0.01 to 5.0% of an organicdisulfide soluble in said vinyl or vinylidene compound and free fromnitro, hydroxyl and primary amino groups on aromatic carbon, theirradiation being of suflicient intensity and employed for a timesuificient to produce substantial polymerization.

In the preferred practice of this invention from 0.1 to 1.0% by weightof a diaryl disulflde, for example, diphenyl disulflde or a diaroyldisuliide, for example, dibenzoyl disulflde, is dissolved inaphotopolymerizable vinyl or vinylidene compound, as above described. Ifdesired, a mutual solvent can also be added to this solution. Thesolution is then placed in a vessel transparent to light of wavelengthsfrom 2500 to 5000 Angstrom units. Borosilicate glass is a satisfactorytransparent material for the construction of suitable containers for thepolymerization reaction mixture. The air over the solution is displacedwith nitrogen, and the vessel and contents are maintained at atemperature of from to 100 C. while exposed to a light source rich inultraviolet light until a substantial degree of polymerization of theunsaturated compound has occurred.

The invention is further illustrated by the following examples in whichparts are by weight.

styrene.

EXAMPLE 1 V under the same conditions for the same length of time buthaving no added agent contains only 7.5% of polymeric styrene. Likewise,a similar sample of styrene containing 1% by weight of benzoyl peroxideirradiated under the same conditions for the same length of timecontains only 33% of polystyrene.

If pure styrene and styrene containing 1% dibenzoyl disulflde are heatedunder an atmosphere of nitrogen at C. for approximately 1'? hours in theabsence of light, both samples contain approximately l'l% polystyrene,respectively.

EXAMPLE II Identical amounts of solutions of styrene each containing 1%by weight respectively of the disulfldes of Table I are placed inborosilicate glass tubes of the same size and shape. The air isdisplaced with nitrogen and the tube is closed. The borosilicate glasstubes containing the various solutions of disulfides in styrene areexposed to the radiation from a mercury lamp watt) at 80 C. and at adistance of 12 inches from the source of radiation. After 6 hours theradiation is stopped and the amount of polystyrene in each sample isdetermined. A sample of styrene containing no added agent is irradiatedunder the same conditions to serve as a control. In Table I below isshown the percent polymer formed in each one of the solutions tested andthe comparative capacity of these disulfides to accelerate the formationof polystyrene is given under the heading Comparative rating." Therelative amount of polymer formed by the use of dibenzoyl disulflde isarbitrarily designated as 1.0.

Tune I Phctopolymeriedtion of styrene at 80 C.

Identical amounts of the vinyl and vinylidene compounds of Table 11below both in the pure state and containing in solution 1% or thedisuliides shown were placed in borosilicate glass tubes 01' the samesize and shape, the air was replaced with nitrogen, the tubes wereclosed, and were irradiated at 25 C. with the light from a mercury lamp(100 watt) placed 12 inches from the tubes. After a suitable periodirradiation was stopped, and the percent polymer obtained was determinedboth for the sample containing the added disulflde and the samplescontaining no added agent. The results are given in the following table.

Tm: H

for 20 hours. The lens produced in this way is advantageous for use insystems subject to severe shock which would shatter inorganic glasslenses.

The photopolymerizable compounds with which this invention is concernedare the photopolymerizable vinyl and vinylidene compounds containing atleast one CHa=C group activated by attachment to a diii'erent negativegroup, that is, halogen, C=O, -CN, C.=.C-, or aryl. These include vinylesters, e.g., vinyl acetate, vinyl propionate; vinyl halides, e.g..vinyl chloride; vinyl ketones. e.g., methyl vinyl ketone; vinyl ethers,e.g.,. vinyl ethyl ether; vinyl cyanides, e.g., acrylonitrile andmethacrylonitrile; esters oi acrylic acid, e.g., methyl acrylate andethylene dlacrylate; styrene; and vinylethinyl carbanols,

vinylidene compounds which can be used are esters of methacrylic acid,e.g., methyl methacrylate, allyl methacrylate, and ethylenedimethacrylate; vinylidene halides, e.g., vinylidene chloride, andesters of alpha-substituted acrylic acids, e.g., methyl alphachloracrylate. Oi these compounds those having a vinyl or vinylidenegroup attached to an aromatic ring, and in particular styrene, arepreferred since the organic disul des are most efl'ectlve in bringingabout satisfactory rate of photopolymerization and in the production ofcolorless products adapted to Photopolymerization of selected vinyl andvinylidene compounds in the presence of organic disulfides at 25 6'.

Methyl Dimethyl t 3255? sense:

Polymer in P0 ymor in Polymer in ymer in cent Pol 7! hrs. 23 his. 75 hm8 hrs, in 22 a 1 None con 1) 0 0 0 I Diben zcyl uliide 21 5 78 is m IDl-gira-tolyl disulilde 74 42 77 4 N, '-dipentamethylene thiuramdisulnde. 7 29 0 N, N'-dimethyl thiuram disulilde 7 Other vinyl andvinylidene compounds likewise show a marked acceleration in their rateof photopolymerization in the presence of an organic disuli'ide. Forexample, at C. under the influence of ultraviolet light acrylonitrilecontaining 1% by weight of dibenzoyl disuli'lde is converted in 2 hoursto a solid white polymer, while a control sample containing no addedagent is unchanged. Similarly, under these conditions allyl methacrylatecontaining 1% dibenzoyl disulflde is converted to a solid polymer in 7.5hours in comparison with an unchanged control sample. Vinyl isobutyrate,methyl acrylate, and n-octyl methacrylate likewise show a markedincrease in the rate or photopolymerization in the presence of 1 byweight of dibenzoyl disulflde over a control sample of these compoundssimilarly irradiated.

EXAMPLEIV Pure monomeric styrene containing 0.5% dibenzoyl disulflde and0.1% benzoyl peroxide by weight is heated at 90C. for 15 hours toproduce a viscous syrup. This syrup is placed in a cell consisting of aglass lens blank and a sheet of plate glass separated by a gasket orrubber tubing coated with polyvinyl alcohol. The syrup is furtherpolymerized to a precisely shaped optical lens by irradiating the syrupin the cell at 75-90 C. with a mercury lamp at a distance of 10 inchesand mixed disuli'ldes containing radicals selected from any of the aboveclasses. Of these disulfldes, best results are obtained with the diaryldisulfides and the diaroyl disulfldes. In general from 0.01 5% by weightof the disulilde based on the vinyl or vinylidene compound can be usedalthough it is preferred to use amounts from 0.1 to 1.0%. The disulfidesmust be soluble in the vinyl or vinylidene compound with which they areused. They must also be free from nitro, hydroxyl and primary aminogroups on aromatic carbon.

The source of radiation is limited only to those providing wave lengthsin the range of 2500-5000 Angstrom units. and preferably in tlie wavelength region of 2800 to 4000 Angstrom units. Sources of radiation thatare commercially available include mercury lamps and arcs. carbon arcs,and hydrogen discharge tubes. Sunlight can also be used as a. source oilight containing the desired wave lengths. Tungsten tensity also ilndutility as light sources.

The photopolymerization can be carried out at temperatures of from to150 C. but in practice the range from 25 to 100 C. is the most useful.Methyl methacrylate operates best at around 25 C. whereas styrenerequires a temperature of from 60 to 80 C. for a sui'flciently rapidpolymerization cycle.

The vessel in which the polymerization is conducted must be transparentto light of the desirable wave lengths when the reaction is conducted sothat the light passes through the sides of the container. It is alsopossible to place the source 01' light directly over the surface of themonomer in a container or within the reaction mixture itself.

The exclusion of oxygen from the photopolymerization systems of thisinvention has been found advantageous and in carrying out thephotopolymerlzation, steps are usually taken to replace the air by aninert gas, for example, nitrogen.

Photopolymerizations in accordance with this process can be carried outin solution, emulsion, or in granular systems. In the preferred process,however, the photopoiymerizable monomer contains in addition to thedisulfide at most only limited quantities oi a mutual solvent.

In some cases, however, it may be desirable to add an organic peroxidecatalyst, for example, benzoyl peroxide, lauroyl peroxide, or diethylperoxide to the Photopolymerization mixture containing the disulfldesince the monomer/disulflde/peroxide combination may be heated to giveviscous casting syrups which when poured into a transparent moldpolymerize rapidly upon exposure to light to give a precisely shapedobject.

This invention is applicable not only to the photopolymerizable vinyland vinylidene compounds above described but also to mixtures thereofand to mixtures of other unsaturated materials photopolymerizable in thepresence of the compounds of this invention.

The products oi this invention are useful as molding powders, adhesives,coating and impregnating agents, transparent resinous enclosures, safetyglass inter-layers, etc. In addition, when photopolymerization of thecompositions is carried out within a mold, useful optical articles suchas lenses, prisms, diffraction gratings, etc. can be obtained. These areless brittle than the inorganic glasses and require no expensive andlaborious grinding procedure. They also have the added advantage ofbeing considerably lighter in weight than the inorganic glasses. Theterm "vinylidene compound" in the claims is inclusive 01' "vinylcompound, 1. e. a vinylidene compound having one of the free valences ofthe vinylidene radical satisfied by hydrogen.

The above description and examples are intended to be illustrative only,and no unnecessary limitations should be understood therefrom.

What is claimed is:

i. A process for preparing polymers which comprises irradiating, withlight of wave length in the lamps oi suiiicient inrange or from 2500 to5000 Angstroms, a composition comprising a photopolymerizable vinylidenecompound having one CH2=C group and that activated by direct attachmentto a diflerent negative group, said group being selected from the classconsisting of halogen, C=O, -C::N, CEC, O, and aryl, and from 0.01 to5%, based on the photopolymerizable compound, 01' an organic disulfldetree from nitro, hydroxyl and primary amino groups on aromatic carbon,the irradiation being of suflicient intensity and employed for a timesuflicient to produce substantial polymerization.

2. A process for preparing polymers of styrene which comprisesirradiating, with light of wave length in the range of from 2500 to 5000Angstrom units, a mixture of monomeric styrene with from 0.01 to 5.0%,based on the styrene, 01 dibenzoyl disulflde, the irradiation being ofsumcient intensity and employed for a time sufllcient to producesubstantial polymerization.

3. A process for preparing polymers which comprises irradiating, withlight of wave length in the range of from 2500 to 5000 Angstrom units, amixture 01' a compound having the vinyl group attached to an arylradical with from 0.01 to 5.0%, based on the vinyl aryl compound, of anorganic disulfide, the irradiation being of suflicient intensity andemployed for a time suilicient to produce substantial polymerization.

4. A process for preparing polymers which comprises irradiating, withlight of wave length in the range 2500-5000 Angstrom units, a mixture ofa photopolymerizable vinylidene compound having but one ethylenic doublebond and that attached to a carbon in turn attached to a differentnegative group, said group being selected from the class consisting ofhalogen, C=O, -CEN, CEc-, -O and aryl, with from 0.01 to 5.0%, based onthe photopolymerizable compound, of an organic disulfide, theirradiation being of sumcient intensity and employed for a, timesufflcient to produce substantial polymerization.

5. Process for preparing polymers which comprises irradiating, withlight of wave length in the range 2500-5000 Angstrom units, a mixture ofa vinyl aryl compound and from 0.01 to 5%, based on the vinyl arylcompound, of a diaroyl disulflde, the irradiation being of sufllcientintensity and employed for a time suflicient to produce substantialpolymerization.

6. Process for preparing polymers which comprises irradiating, withlight of wave length in the range 2500-5000 Angstrom units, a mixture ofa vinyl aryl compound and from 0.01 to 5%, based on the vinyl arylcompound, of a diaryl disulflde, the irradiation being of sufficientintensity and employed for a time suflicient to produce substantialpolymerization.

7. A process for preparing styrene polymers which comprises irradiatinga mixture of styrene and from 0.01 to 5% based on the styrene, of adiaroyl disulflde with light of wave length of 2500-5000 Angstrom units,the irradiation being of sufllcient intensity and employed for a timesufficient to produce substantial polymerization.

8. A process for preparing styrene polymers which comprises irradiatinga mixture of styrene and from 0.01 to 5%, based on the styrene, of adiary] disulflde with light of wave length of 2500-5000 Angstrom units,the irradiation being of suflicient intensity and employed for a timesuiiicient to produce substantial polymerization.

9. A process for preparing polymers oi styrene which comprisesirradiating, with light of wave length in the range 01 tram 2600-5000Angstrom units, a mixture of monomeric styrene with from 0.01 to 0.0%.based on the styrene. o1 di-parstolyl disuiiide, the irradiation beingor sumcient intensity and employed lo:- a time suiiicient to producesubstantial polymerisation.

10. A process for preparing polymers of styrene which comprisesirradiating with light in the ultraviolet range. a mixture of monomericstyrene, with from .196 to 5.0%, based on the weight of styrene, ofdibenzoyl clisulnde, the irradiation being of sumcient intensity andemployed for a time sufllcient to produce substantial polymerization.

LAWRENCE MARION RICHARDS.

The following references are of record in the tile 01 this patent:

UNITED STATES PATENTS OTHER C38 Chemical Action of Ultraviolet Boys,"1941, pages 131 to 134 sud-406 to 412, Ellis and Wells. ReinholdPublishing Corp., 330 W. 42d Bt., New York. N. Y.

